[2.0 Proposition] Rename vorpal.catch to avoid Promise ambiguity

I think we should take benefit of the [inbuilding v2](https://github.com/dthree/vorpal/pull/272) to rename the `.catch()` commands.
One of the reason is that is connote a promise method, error handling of other command.
Besides it's usage is wrongly flagged as error by the [common used promised eslint config](https://github.com/xjamundx/eslint-plugin-promise) with rule `promise/catch-or-return`

I'm not sure on which name we should use, but something around `miss` like `onCommandMiss`, or `onNonMatchingCommand`, or maybe better and simpler`fallback`